Interaction of Combustion with Transverse Velocity Fluctuations in Liquid Rocket Engines

Abstract

The verification of thermoacoustic stability is one of the most essential steps in the framework of the development of liquid rocket engines. In hybrid methods, which allow fast and detailed evaluation of the flame/acoustics interaction, the simulation of wave propagation is separated from the analysis of flame response to acoustic perturbations. This requires a feedback model for the interaction of combustion and acoustics. Transverse modes, which are particularly prone to combustion instabilities due to their low nozzle damping, are dominated by velocity fluctuations in the transverse direction. The interaction of these fluctuations with the combustion process in liquid rocket engines is numerically studied in the paper, employing a rocket engine configuration with hypergolic propellants as an example. It is shown that the fluctuations lead to major changes in the mean flow near the injector as evaporation and mixing are accelerated. Furthermore, the study reveals that the displacement of the flame center has a substantial thermoacoustic coupling potential. With forced single-flame computations, the strong slip between the flame motion and the acoustic velocity is analyzed. On the basis of the findings from the flame dynamics study, a feedback model to be used in stability analyses with hybrid methods is proposed, which allows one to take the flame dynamics originating from periodic flame displacement into account.